The present invention relates to lock-out mechanisms for limiting the stroke of actuators or the like and particularly to such a lock-out mechanism as may be employed with railroad type empty/load control valves.
In the railroad industry, empty/load control valves are typically employed on freight cars having high gross to tare weight ratios, the purpose being to automatically reduce the car brake pressure under "empty" car load conditions, in order to prevent the occasion of wheel slide due to excessive brake force, particularly under heavy service and emergency braking.
The "empty" or "load" condition of a freight car is typically determined by sensing the car spring deflection, which indirectly reflects the weight of car lading, or by sensing the pressure of lading on a slope sheet on hopper type cars, which directly reflects the weight of the car load. Spring deflection may be detected by means of a car-body-mounted empty/load valve having a sensing arm adapted to engage the car truck during a brake application. Alternatively, the empty/load valve may be truck-mounted with the sensing arm arranged to engage the car body. Slope sheet pressure may be detected by a sensing rod that contacts a deflectable membrane forming part of the slope sheet. The sensing rod measures the deflection of the membrane in accordance with the weight of the car lading and accordingly positions a spool within the empty/load valve that is mounted on the slope sheet generally in concentric relationship with the deflectable membrane.
Under certain conditions, it is desirable to disable the empty/load valve in order to prevent an "empty" car load condition from being detected, such as in carrying out brake tests and/or when setting up a slack adjuster, the desideratum being to achieve normal brake pressure.
Where empty/load valves are employed in a manner to detect spring deflection indicative of the car weight, the empty/load valve is typically disabled by strategically locating a block of wood or the like, between the sensing arm and car body or truck, as the case may be, so as to cause a false reading by the sensing arm.
Where empty/load valves are utilized in slope sheet configurations, a plug is generally removed from an access hole in the empty/load valve to accommodate insertion of various devices for jamming the sensing rod to thereby lockup the valve in its "load" setting.
Such disabling methods are not only laborious and time consuming, but there is no guarantee that the operator/tester conducting the brake test or slack adjuster set-up will remember to restore the disabled valve to its operative condition. Such an oversight, of course, can have serious consequences, since full "load" brake pressure would then be available for braking an "empty" weight car, resulting in the likelihood of wheel damage due to sliding wheels.